The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 100 24 296.0, filed on May 17, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a machine for producing a material web, in particular a cardboard or paper web, with at least one smooth roll wrapped by the material web.
2. Discussion of Background Information
In the multi-cylinder drying section of a paper machine, the paper web is guided over steam-heated cylinders or steam-heated cylinders and wire suction rolls for the purpose of drying the web. Especially at the beginning of the drying process, when the moist paper does not yet have sufficient strength, problems often occur with regard to the web guidance, which can especially be attributed to the fact that the moist web sticks to the smooth surfaces, which are absolutely necessary for good heat conduction, and the web is poorly ventilated. In order to be able to remove the web from the cylinders, a sufficient web tension is necessary, which can only be produced by means of pulling, i.e., a corresponding differential speed, before or directly after the first smooth contact surface. This often causes tears and an overstretching of the edges. Because these problems occur more intensely at higher speeds and the tension must be increased, the speed of the paper machine is limited.
An aspect of the invention is to create an improved machine of the type mentioned at the outset in which the above-mentioned problems are eliminated. Here, it should particularly be achieved that the amount of pulling and/or web tension necessary for removing the web from the smooth roll is reduced.
This aspect is attained according to the invention in that a blowing device is assigned to the roll, whose discharge stream is directed into the wedge-shaped opening between the roll and the material web, for the purpose of ventilating the web. Here, the discharge stream of the blowing device is preferably pointed directly into this wedge-shaped opening.
Because of this construction, an improved ventilation of the material web results, whereby the removal of the web sticking to the roll is facilitated. The blowing device can, in particular, be supplied with air. Preferably, the blowing device includes several discharge openings, in particular, embodied as nozzles, blowing holes, blowing slits, and/or the like.
In a preferred practical embodiment of the machine according to the invention, the blowing device includes at least one blowing tube. The blowing device can extend at least essentially over the entire web width. The discharge stream directed into the wedge-shaped opening of the blowing device is preferably directed slightly against the roll surface.
It is advantageous for the blowing speed of the discharge stream directed into the wedge-shaped opening to be variably adjustable. It can preferably be selected depending on the distance of the blowing device from the wedge-shaped opening. For example, the greater the distance from the wedge-shaped opening, the greater the blowing speed of the discharge stream must be.
The distribution of the discharge openings of the blowing device can vary over the web width. Thus, for example, the distance of the discharge openings in the edge region can be greater than or less than in the middle region. Here, the distance of the discharge openings in the edge region can be greater than or less than in the middle region. Correspondingly, the ventilation can optimally be adapted to the respective conditions such that excessive amounts of air can be prevented.
The blowing device can be integrated into a doctor assigned to the roll or can be attached to such a doctor such that a transfer from the doctor is possible, which means that the web does not run between the doctor and the blowing device in the case of a tear.
It is useful to provide the blowing device with a cover in order to ensure a sufficient protection, in particular from paper scraps. Thus, the possibility of the blowing device becoming a scrap catcher is eliminated.
The position of the doctor should be selected such that, on the one hand, it is arranged sufficiently close to the wedge-shaped opening to ensure sufficient ventilation, and on the other hand, is arranged at a sufficient distance from the wedge-shaped opening to prevent a blockage in the case of a tear.
It is useful to select the size and/or number of discharge openings of the blowing device depending upon the machine speed, the basis weight, the stock, and/or the paper type. Here, the discharge openings, which are, for example, circular, can have a diameter that, in particular, lies in the range of approximately 2 to approximately 12 mm and preferably in the range of approximately 4 to approximately 8 mm.
The blowing speed of the discharge stream of the blowing device is preferably greater than approximately 35 m/s and preferably greater than approximately 50 m/s. Optimal results can especially be achieved at higher air speeds using smaller amounts of air, i.e., no larger amounts of air are necessary.
The rolls in question can be formed, for example, by a drying cylinder. Here, the blowing device is usefully structured and/or insulated such that a thermal deformation and a deviation from the desired blowing direction caused thereby are excluded.
In a useful embodiment, the blowing device simultaneously serves the ventilation of one of the rolls and a hood assigned to the drying cylinder. It can be operated at the air inlet temperature of the hood.
In a preferred embodiment of the machine according to the invention, the roll is formed by the first cylinder of the drying section. However, it is also possible to assign a corresponding blowing device to at least one of the second to fifth cylinders of the drying section.
In a further advantageous embodiment, the roll is formed by a smooth pressing roll. In principle, however, at least one further cylinder and/or at least one further smooth roll can have a corresponding blowing device assigned to it.
According to an aspect of the present invention, the discharge stream of the blowing device is pointed directly into the wedge-shaped opening. According to another aspect of the present invention, the blowing device is supplied with pressurized air. In yet another aspect of the present invention, the blowing device includes several discharge openings formed in particular by nozzles, blowing holes, blowing slits, and/or the like.
In yet another aspect of the present invention, the blowing device includes at least one blowing tube. According to a further aspect of the present invention, the blowing device extends at least essentially over the entire width of the web. In another aspect of the present invention, the discharge stream of the blowing device, which is pointed into the wedge-shaped opening, is pointed slightly against the roll surface.
In another aspect of the present invention, the blowing speed of the discharge stream may be variably adjusted. According to a further aspect of the present invention, the blowing speed of the discharge stream may be selected depending on the distance of the blowing device from the wedge-shaped opening.
According to a still further aspect of the present invention, the distribution of the discharge openings of the blowing device varies over the web width. Other aspects of the invention include the distance of the discharge openings in the edge regions differing from that in the middle regions.
Further aspects of the invention include wherein the distance of the discharge openings in the edge region is less than in the middle region. According to other aspects of the present invention, the distance of the discharge openings in the edge region is greater than in the middle region.
According to another aspect of the present invention, the blowing device is integrated into a doctor assigned to the roll or is attached to such a doctor. According to a further aspect of the present invention, the blowing device is provided with a covering.
In yet another aspect of the invention, the size and/or the number of the discharge openings is selected depending on the machine speed, the base weight, the stock, and/or the paper type. In another aspect of the present invention, the discharge openings, which are circular, for example, have a diameter that lies in a range of approximately 2 to approximately 12 mm and preferably in a range of approximately 4 to approximately 8 mm.
According to a further aspect of the present invention, the blowing speed of the discharge stream of the blowing device is greater than approximately 35 m/s and preferably greater than approximately 50 m/s. In another aspect of the present invention, the roll is formed by a drying cylinder.
According to a still further aspect of the present invention, wherein at the same time, the blowing device serves to ventilate a hood assigned to the roll and/or the drying cylinder. According to a still further aspect of the present invention, the blowing device is operated at the air inlet temperature of the hood. Other aspects of the invention include wherein the roll is formed by the first drying cylinder of a drying section.
Further aspects of the invention include a corresponding blowing device is assigned to at least one of the second to fifth cylinders of a drying section. According to another aspect of the present invention, the roll is formed by a smooth pressing roll. According to a further aspect of the present invention, the blowing device has various zones in the crosswise direction, for example, special zones for the edges. According to a still further aspect of the invention, the blowing device only blows onto the edges.
According to another aspect of the present invention, a machine for producing a material web having at least one smooth roll at least partially wrapped by the material web is provided. The machine includes an air blowing device arranged for ventilating the material web with at least one discharge stream, wherein the at least one discharge stream is directed into a wedge-shaped opening formed between the at least one at least one roll and the material web leaving the roll.
In yet another aspect of the invention, the material web is one of a cardboard or paper web. Additionally, other aspects of the present invention includes wherein the blowing device has at least one discharge opening arranged to form the at least one discharge stream. In another aspect of the present invention, the distance between the discharge openings in the edge regions is less than the distance between the discharge openings in the middle region.
According to a further aspect of the present invention, the distance between the discharge openings in the edge region is greater than the distance between the discharge openings in the middle region.
According to a further aspect of the present invention, at least one of the size and number of the discharge openings is selected depending on at least one of machine speed, basis weight of the material web, the stock, and paper type.
In another aspect of the present invention, the roll includes a drying cylinder. According to a still further aspect of the present invention, at the same time, the blowing device serves to ventilate a hood assigned to at least one of the roll and drying cylinder. In another aspect of the present invention, the roll includes a first drying cylinder of a drying section.
Other aspects of the invention includes wherein the blowing device has various zones in a crosswise direction, with respect to the material web. Further aspects of the invention include various zones which include special zones for edges of the material web. According to other aspects of the present invention, the blowing device only blows onto edges of the material web.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.